The present invention relates to hollow cylindrical rotors for regenerative heat exchangers and more particularly to such a rotor comprising an outer casing which comprises a plurality of layers of a helically wound strip orientated so that its width direction is radial with respect to the rotor, a core on which the strip is wound and which is permeable for the medium with which the rotor is to be used, said strip having channels therein to allow the radial passage of the current of the medium.
Such a rotor has been proposed in the German Pat. No. 3,308,445 with the aim of providing a heat exchanger which on the one hand had a high flow and thermal efficiency and on the other hand was able to be simply produced. In order to achieve this object the strip was so designed that the recesses or grooves therein only extended over a fraction of its height and formed the channels in the individual layers of the strip, which were placed in sealing contact with each other so that flow in the circumferential direction was prevented. For shaping the strip while being wound on a drum it was run between embossing rolls with complementary outer faces, the shaped or embossed strip then being continuously wound onto a core taking care to see that the channels of the consecutive layers were precisely aligned in relation to each other in order to ensure the passage of the flow of medium therebetween. However such a structure could only be produced by a machine moving in steps and with a high degree of accuracy. If the required degree of precision was not kept to while winding the strip on the core the resulting structure would interfere with the flow of the medium.